Attaining Hypersonic Flight with Aluminum-Based Fuel-Rich Propellant

Abstract

In this paper, experimental results of an aluminized fuel-rich propellant having energetics similar to boron-based fuel-rich propellant and having no residue after combustion are discussed. Using this aluminum-based fuel-rich propellant, which has higher density than the current fuels used for hypersonic flight, this paper looks at enhancing the Mach number envelope of a ramjet. Nondimensional thrust and drag calculations were carried out to identify the air–fuel ratio required for a Mach 6 flight, with different intakes accounting for different pressure recovery. Calculations were carried out with three different intakes, and it was observed that, even with the lowest pressure recovery of 9% at Mach 6, a hypersonic mission was possible. Values for various efficiencies were chosen with great care, and a perturbation analysis was carried out to make the calculations more robust. The specific impulse obtained with the aluminum-based fuel-rich propellant in ramjet mode was 515 s at a 25 km altitude. Comparison of an aluminum-based fuel-rich propellant in ramjet mode was made with a kerosene and hydrogen fueled scramjet from the specific impulse data available in the literature. The specific impulse of the aluminum-based fuel-rich propellant was nearly an order of magnitude higher as compared to a hydrogen fueled scramjet when adjusted to the density of hydrogen. Upon considering a system size, it was also shown that the aluminum-based fuel-rich propellant could meet the burn rate requirement for a Mach 6 flight.